import os

os.chdir("C:/workspace/data/uis")

for f_name in os.listdir():
    f_in = open(f_name, 'r')
    lines = f_in.readlines()
    f_in.close()
    
    f_out = open(f_name, 'w')
    for line in lines:
        line = line.replace("::", ":NULL:")
        f_out.write(line)
        
    f_out.close()
    